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Rev. 8
C. Adjust/Test the Blind Altitude Encoder
The encoder will not give an output until it has the correct operating temperature. If the power
goes off and then on again, a delay of 6 minutes occurs. The approximate warm-up times are:
− From 70°F (21°C) 4 to 6 minutes.
− From 0°F (-18°C) Up to 10 minutes.
− From -55°F (-48°C) 30 to 45 minutes.
The adjusters are adjacent to the static port on the encoder. The LO adjuster is towards the
outside. The HI adjuster is towards the center.
Detail Steps/Work Items Key Items
(1) Connect the test equipment. Refer to the equipment manufacturers
manuals.
(2) Set the airplane altimeter to 29.92 in.Hg.
(3) Monitor the altitude code. Decrease
pressure until the output code just changes
to 20000 ft
(4) Make sure that the altimeter reading is within
±125 ft of the encoder reading. If not, adjust
the HI adjuster until the change occurs within
30 ft of the altimeter reading.
Lightly tap the altimeter to prevent errors
due to friction.
(5) Increase the pressure until the output code
just changes to 0 ft.
(6) Make sure that the altimeter reading is within
±125 ft of the encoder reading. If not, adjust
the LO adjuster until the change occurs
within 30 ft of the altimeter reading.
Lightly tap the altimeter to prevent errors
due to friction.
(7) Do steps 2 to 5 again until both the 20000 ft
and 0 ft values are within the ±125 ft
tolerance
(8) Operate the system through the range of 0 ft
to 20000 ft. Make sure that the altimeter and
encoder are within the ±125 ft tolerance.
Lightly tap the altimeter to prevent errors
due to friction.
(9) Remove the test equipment.
DA20-C1 AMM
Navigation
Doc # DA 201-C1
Rev. 8 34-10-00 Page 209
24 Oct 2001
6. Remove/Install the OAT Indicator
A. Remove the OAT Indicator
Detail Steps/Work Items Key Items
(1) Open the OAT circuit-breaker.
(2) Remove the instrument panel cover. Refer to Chapter 25-10
(3) Remove the nut from the temperature
sensor.
In the right NACA duct.
(4) Remove the temperature sensor lead from
the cable harness and disconnect the
electrical connector for the power supply.
(5) Remove the OAT indicator and sensor from
the airplane.
B. Install the OAT indicator
Detail Steps/Work Items Key Items
(1) Put the OAT indicator in position in the
instrument panel.
(2) Connect the electrical connector for the
power supply.
(3) Put the temperature sensor in position.
Attach the sensor with the nut.
In the right NACA duct.
(4) Tie the temperature sensor lead to the wiring
harness.
(5) Close the OAT circuit-breaker.
(6) Set the GEN/BAT switch to ON. The OAT indicator must indicate the
ambient temperature ± 1%.
(7) Set the GEN/BAT switch to OFF.
(8) Install the instrument panel cover. Refer to Chapter 25-10
Navigation
DA20-C1 AMM
Page 210
24 Oct 2001 34-10-00 Doc # DA 201-C1
Rev. 8
7. Pitot and Static Leak Tests
Always do a pitot leak-test after you do maintenance on the pitot system. And always do a lowrange
static leak-test after you do maintenance on the static system.
CAUTION: OBEY THE FOLLOWING PRECAUTIONS WHEN YOU DO A PITOT OR
STATIC LEAK-TEST. IF YOU DO NOT OBEY THE PRECAUTIONS,
YOU CAN DAMAGE THE AIR DATA INSTRUMENTS.
A. Test Precautions
− The pressure in the pitot system must be equal to (or greater than) the pressure in the static
system.
− Reversal of the pitot and static pipes can cause damage to the air data instruments.
− The applied pressure (and rate of change of pressure) must not be greater than the design
limits of the equipment under test.
− After doing the test, you must return the system to its usual operating conditions.
B. Equipment
Item Quantity Reference
Pitot-static probe adaptor 1 65797-07
Pitot-static leak-tester 1 Commercial
DA20-C1 AMM
Navigation
Doc # DA 201-C1
Rev. 8 34-10-00 Page 211
24 Oct 2001
C. Low-Range Static Leak-Test
Follow the test-equipment manufacturer’s instruction for the use of the test equipment.
Detail Steps/Work Items Key Items
(1) Obey the precautions at the beginning of this
subject.
(2) Connect the pitot-static leak-tester to the
pitot-static probe.
(3) Apply a partial vacuum to the static port until
you get a pressure altitude of 1000 ft above
the ambient pressure altitude.
Note the altitude.
(4) Let the pressure stabilize.
(5) Monitor the system pressure. The pressure loss must not be more than
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